System and method for annotating an electronic document independently of its content

ABSTRACT

A system, method, and apparatus for annotating an electronic document independently of its content is provided. According to one variation, a tablet and stylus-based computer is programmed with a document browser that permits a user to annotate documents viewed through the browser. The annotations are stored separately from the viewed document pages but are correlated with the pages such that when a previously annotated page is revisited, annotations relating to that page are retrieved and displayed on top of the page as an “ink” layer. Three different annotation modes are possible: ink, highlight, and erase. Each mode can be selected through a user interface supplied through the browser or through controls embedded in a document.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/964,457, filed on Dec. 26, 2007, now issued as U.S. Pat. No.7,975,216, which is a continuation of U.S. patent application Ser. No.09/455,805, filed on Dec. 7, 1999, now issued as U.S. Pat. No.7,337,389, both of which are incorporated herein by reference.

TECHNICAL FIELD

This invention relates generally to document browsers and pages that aredisplayed using such browsers. More particularly, the invention providesa method and apparatus for allowing a user to add annotations and othermarkings to an electronic document independently of the content of thedocument.

BACKGROUND OF THE INVENTION

Web browsers are conventionally used to display documents created with astandard descriptive language such as Hyper Text Markup Language (HTML).Documents written in such languages can be displayed with various visualand audio effects such as color, animation, sound effects, and the like.The documents may include text, bitmap images, graphics, and other typesof content.

Web browsers (or, more generally, “document browsers”) typically providefunctions which permit a user to advance forward and backward among aseries of related pages; to jump to a specified page; to jump to pagesthat are referenced via a so-called “hyperlink” embedded in a page; andto maintain a list of recently viewed pages. Although frequently used tonavigate through web pages on the Internet, document browsers can beused to display pages that reside on a local area network or even alocal computer on which the browser executes.

Recently, as computers have become smaller, it has become possible torun browsers on notebook computers, palm-sized computers, and so-called“tablet and stylus” computers. The latter devices typically comprise athin computer roughly the size of a sheet of paper with a large writingsurface that doubles as a display, and a stylus that substitutes for akeyboard. A user can display and edit documents using the stylus as awriting instrument.

One potential application for such hand-held computers is the display ofmass-produced documents such as books, maps, and other descriptivematerial. For example, a user who purchases a textbook or fictional workon a CD-ROM or other medium can display the work using a small computersuch as a tablet-based computer.

In some instances, a user may want to annotate or otherwise mark pagesdisplayed on the computer. Using a conventional word processing program,a user can rearrange text, highlight certain words or phrases, or deleteportions of the text. Such features require that the user have access tothe underlying content (e.g., the descriptive material that forms thework). In the case of copyrighted materials, however, editingcapabilities may not be available to modify the underlying materials.Certain text may be copy-protected or otherwise unavailable for editingusing normal editing tools, or may not be in a format suitable for wordprocessing. In such circumstances, there may be no practical way for auser to annotate such works. As one example, a student viewing a copy-or edit-protected textbook on a tablet-based computer may have nopractical way of making notes directly in the textbook. Such a featurewould be desirable notwithstanding the copy protection or unavailabilityof general editing functions for the document.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for users toannotate documents in a document browser without changing the contentsof the documents. According to one variation of the invention, a tabletand stylus-based computer is programmed with a document browser thatpermits a user to annotate documents that are viewed through thebrowser. The annotations are stored separately from the viewed documentpages but are correlated with the pages such that when a previouslyannotated page is revisited, annotations relating to that page areretrieved and displayed on top of the page as an “ink” layer.

According to one variation of the invention, three different annotationmodes are provided: ink, highlight, and erase. Each mode can be selectedthrough a user interface supplied through the browser or throughcontrols embedded in a document. The annotation functions can beimplemented as an Active-X® control, as an Applet, or as dedicated codeintegrated into the browser. Other features and advantages of theinvention will become apparent through the following description, thefigures, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a conventional general-purpose computing environment thatcan be employed in various embodiments of the invention.

FIG. 2 shows a conventional tablet and stylus-based computer that can beused according to one aspect of the invention.

FIG. 3 is a conceptual view showing an ink layer 302 arranged on top ofan underlying document page 301. The ink layer may include opaque andtranslucent markings.

FIG. 4 shows a user interface on a computer screen including a menu 402that permits a user to select from among a plurality of annotation modeson a displayed document.

FIG. 5 shows a user interface on a computer screen including an opaqueannotation 501 and a highlighted annotation 502, both superimposed overa displayed document.

FIG. 6 shows a user interface on a computer screen including an opaqueannotation 601 in a pre-erase state.

FIG. 7 shows a user interface on a computer screen including an opaqueannotation 701 in a post-erase state, where the annotation has beenpartially erased.

FIG. 8 shows one possible software design for implementing variousprinciples of the invention.

FIG. 9A shows a flowchart indicating various steps that can be executedto provide an annotation function according to certain inventiveprinciples.

FIG. 9B shows a flowchart indicating how previously created annotationscan be superimposed over a document page.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic diagram of a conventional general-purpose digitalcomputing environment that can be used to implement various aspects ofthe invention. Computer 100 includes a processing unit 110, a systemmemory 120, and a system bus 130 that couples various system componentsincluding the system memory to the processing unit 110. The system bus130 may be any of several types of bus structures including a memory busor memory controller, a peripheral bus, and a local bus using any of avariety of bus architectures. The system memory includes read onlymemory (ROM) 140 and random access memory (RAM) 150.

A basic input/output system 160 (BIOS), containing the basic routinesthat help to transfer information between elements within the computer100, such as during start-up, is stored in ROM 140. Computer 100 alsoincludes a hard disk drive 170 for reading from and writing to a harddisk (not shown), a magnetic disk drive 180 for reading from or writingto a removable magnetic disk 190, and an optical disk drive 191 forreading from or writing to a removable optical disk 192 such as a CD ROMor other optical media. The hard disk drive 170, magnetic disk drive180, and optical disk drive 191 are connected to the system bus 130 by ahard disk drive interface 192, a magnetic disk drive interface 193, andan optical disk drive interface 194, respectively. The drives and theirassociated computer-readable media provide nonvolatile storage ofcomputer readable instructions, data structures, program modules andother data for the personal computer 100. It will be appreciated bythose skilled in the art that other types of computer readable mediawhich can store data that is accessible by a computer, such as magneticcassettes, flash memory cards, digital video disks, Bernoullicartridges, random access memories (RAMs), read only memories (ROMs),and the like, may also be used in the exemplary operating environment.

A number of program modules can be stored on the hard disk, magneticdisk 190, optical disk 192, ROM 140 or RAM 150, including an operatingsystem 195, one or more application programs 196, other program modules197, and program data 198. A user can enter commands and informationinto the computer 100 through input devices such as a keyboard 101 andpointing device 102. Other input devices (not shown) may include amicrophone, joystick, game pad, satellite dish, scanner, or the like.These and other input devices are often connected to the processing unit110 through a serial port interface 106 that is coupled to the systembus, but may be connected by other interfaces, such as a parallel port,game port or a universal serial bus (USB). A monitor 107 or other typeof display device is also connected to the system bus 130 via aninterface, such as a video adapter 108. In addition to the monitor,personal computers typically include other peripheral output devices(not shown), such as speakers and printers.

The computer 100 can operate in a networked environment using logicalconnections to one or more remote computers, such as a remote computer109. Remote computer 109 can be a server, a router, a network PC, a peerdevice or other common network node, and typically includes many or allof the elements described above relative to computer 100, although onlya memory storage device 111 has been illustrated in FIG. 1. The logicalconnections depicted in FIG. 1 include a local area network (LAN) 112and a wide area network (WAN) 113. Such networking environments arecommonplace in offices, enterprise-wide computer networks, intranets andthe Internet.

When used in a LAN networking environment, the computer 100 is connectedto the local network 112 through a network interface or adapter 114.When used in a WAN networking environment, the personal computer 100typically includes a modem 115 or other means for establishing acommunications over the wide area network 113, such as the Internet. Themodem 115, which may be internal or external, is connected to the systembus 130 via the serial port interface 106. In a networked environment,program modules depicted relative to the personal computer 100, orportions thereof, may be stored in the remote memory storage device.

It will be appreciated that the network connections shown are exemplaryand other means of establishing a communications link between thecomputers can be used. The existence of any of various well-knownprotocols such as TCP/IP, Ethernet, FTP, HTTP and the like is presumed,and the system can be operated in a client-server configuration topermit a user to retrieve web pages from a web-based server. Any ofvarious conventional web browsers can be used to display and manipulatedata on web pages.

FIG. 2 shows a tablet and stylus computer that can be used in accordancewith various aspects of the present invention. Any or all of thefeatures, subsystems, and functions in the system of FIG. 1 can beincluded in the computer of FIG. 2. Computer 201 includes a largedisplay surface 202 (e.g., a flat panel display) on which a plurality ofwindows 203 is displayed. Using stylus 204, a user can select,highlight, and write on the display area. Computer 201 interprets marksmade using stylus 204 in order to manipulate data, enter text, andexecute conventional computer application tasks such as spreadsheets,word processing programs, and the like. One commercially availabletablet and stylus computer incorporating many of these features is theStylistic 2300 computer sold by Fujitsu Personal Systems, Inc., of SantaClara, Calif.

A stylus could be equipped with buttons or other features to augment itsselection capabilities. In one embodiment, a stylus could be implementedas a “pencil” or “pen” in which one end constitutes a writing portionand the other end constitutes an “eraser” end which, when moved acrossthe display, indicates that portions of the display are to be erased.Other types of input devices such as a mouse, trackball, or the likecould be used. Additionally, a user's own finger could be used to selector indicate portions of the displayed image on a touch-sensitive orproximity-sensitive display. Consequently, the term “user input device”is intended to have a broad definition and encompasses many variationson well-known input devices.

FIG. 3 is a conceptual view showing a computer screen on which adocument page 301 is displayed using a document browser. As isconventional, the document page contains text and/or graphics ofinterest to the user (i.e., “content”). In accordance with theinvention, a special “ink” layer 302 is superimposed over the documentpage 301. Using stylus 305, the user can highlight certain parts of thedocument 304, which are then shown in a highlighted color (e.g., yellow)against the background text.

Also using stylus 305, the user can mark opaque annotations 303 on thecomputer display, which appear to be written on the page itself.(Although ink layer 302 is shown as a separate layer in FIG. 3, thisview is for conceptual purposes only; the user would see only documentpage 301 with annotations superimposed over the text and/or graphics onthe page). According to one aspect of the invention, annotations made bya user on document page 301 are maintained as a separate “ink” layer 302that is superimposed over and blended with pixels on the document page.Consequently, even though the annotations appear to be made directly onthe underlying document, they are actually maintained in a separatedisplay layer blended with the document page being viewed.

In one embodiment, annotations are specific to each user, such thatother users who view the same document will not see a previous user'sannotations. This feature can be implemented using log-ins or other useridentifiers. For an identical document retrieved at two different remotecomputers each having the inventive features, annotations made on oneremote computer would not show up on the other remote computer, sincethe annotations are made independently of the document content. It is,however, within the scope of the invention to permit sharing ofannotations if desired.

Although the inventive principles are described with respect to a tabletand stylus computer, these principles can be applied to other types ofcomputers, including desktop systems, notebook computers, and the like.Many types of input devices, such as touch-sensitive displays and thelike, can be used to indicate those portions of the display that are tobe annotated. Moreover, as explained above, many variations on a basicstylus are of course possible, including an embodiment in which thestylus includes a writing end and an “erasing” end.

FIG. 4 shows a user interface on a computer screen on which a documentpage 401 is displayed using a document browser. In accordance with oneembodiment of the invention, the user interface includes an annotationmode selection menu 402 that permits a user to select from among aplurality of annotation modes for a displayed document. By tapping thestylus on pen button 403, the user can cause the annotation modeselection menu 402 to be displayed. A mode indicator 404 indicates thecurrent annotation mode for the document browser.

According to one variation of the invention, these modes can include an“ink” mode, a “highlight” mode, and an “erase” mode. Additionally, a“selection” mode permits the user to switch to normal browser functions.As shown in FIG. 4, the user interface is already in “erase” mode(indicated by mode indicator 404), so that “erase” is not shown as oneof the available modes in menu 402.

It is not necessary to provide an explicit “mode selection” feature asdescribed above; instead, mode selection can be implicit in the mannerby which the input device is used. As one example, a stylus could beused to provide an ink mode when the stylus is used as a writingimplement; a highlighting mode when the stylus is held a certain way orwhen a button is pressed on the stylus; and an erase mode when an“erasing” end of the stylus is moved across portions of the display. Asanother example, one of the modes (e.g., the ink mode) could beestablished as a default mode when a user input device is manipulated,with other modes being selected based on additional user inputs ormanipulations or even voice commands, for example. Many other variationsare of course possible.

FIG. 5 shows a user interface on a computer screen including thedocument of FIG. 4. Using the “ink” mode, the user has annotated aportion of the document 501 with an opaque ink color (e.g., black orblue). The user has also highlighted a different portion of the document502 using the “highlight” mode. The highlighted portion 502 appears in atranslucent color (e.g., yellow) superimposed over the underlyingdocument. Using the “ink” and “highlight” modes, the user is able toannotate pages viewed through the document browser as needed.

FIGS. 6 and 7 show one possible approach for implementing an “erase”mode. FIG. 6 shows a pre-erase screen in which the user has annotated adocument page using an opaque ink color 601. FIG. 7 shows the samescreen of FIG. 6 after the user has selected the “erase” mode and movedthe stylus across a portion of the annotated region 601, leaving apartially erased annotation 701. Using the “erase” mode, the user canremove previous annotations from the computer screen. The width of theeraser function can be varied to suit various applications, or it caneven be user-selectable.

FIG. 8 shows one possible software design for implementing variousprinciples of the invention. As shown in FIG. 8, a document browser 801permits a user to retrieve and view content in the form of documentsfrom a document storage area 804. The documents can be stored locally onthe user's computer (e.g., on CD-ROM disks and the like), or they can bestored remotely and retrieved across a network such as the Internet.Annotation editor 803 retrieves and stores annotations in “ink layers”stored in a storage device or area 805. As with document storage, inklayer storage area 805 can be local or remotely located.

Annotations retrieved from storage area 805 are provided to pixelblending function 802, which is indicated as a newly provided functionwithin document browser 801. Alternatively, pixel blending function 802can be provided separately (e.g., in the operating system, for example).In general, pixel blending function 802 blends pixels from a documentpage with corresponding pixels from an annotation or “ink” layer mappedto that document page, and generates a blended pixel image that isdisplayed as an annotated document page 806.

In one embodiment, each opaque annotation pixel replaces a correspondingpixel on a document page, whereas each translucent annotation pixel(e.g., highlighting) is blended with a corresponding pixel value on adocument page to produce a different color from that in the originaldocument. Pixel blending functions such as alpha blending are well knownand no further elaboration of this feature is required.

Annotations can be saved as “strokes” in a data structure and storedlocally in a file associated with the currently displayed page of thedocument. Each stroke can comprise a stroke type (e.g., annotate,highlight or erase), a stroke width, and a stroke color in addition tocoordinates indicating the stroke trajectory. In various embodiments,annotation storage occurs automatically, such that whenever the inputdevice is released (or lifted), a new stroke is automatically stored.

Alternatively, it is of course possible to store annotations as a bitmapimage having the same or similar dimensions as the presently displayeddocument page, such that the annotation image can be superimposed overthe document page. Combinations of these approaches are of coursepossible. For example, opaque annotations could be stored in a datastructure, while highlighting could be stored as a bitmap image.

According to one embodiment, document browser 801 generates a titlechange event to annotation editor 803 each time a different documentpage is selected through document browser 801. This permits annotationeditor 803 to retrieve previously stored annotations for a page, and tocreate a new annotation file for a newly displayed page. Annotationeditor 803 intercepts stylus movements from a stylus or other cursormovement device and provides them to document browser 801 after anyannotation processing has been performed. In one embodiment, browser 801can constantly generate “screen paint” commands that are intercepted sothat a blended image is continuously generated.

Annotation editor 803 can be implemented as an Active-X® controlelement, as an Applet, or as other forms of software functions.Annotation editor 803 and any related functions can be embedded into adocument viewed through browser 801, such that viewing the documentprovides the annotation functions.

FIG. 9A shows a flowchart indicating various steps that can be executedto provide an annotation function according to one embodiment. It willbe appreciated that many different approaches for carrying out theinventive principles are possible, and the steps shown are intended tobe exemplary only. For example, although the steps are illustrated asbeing performed sequentially, they can in fact be performed by differentcomponents at different times in an object-oriented system usingevent-driven processing techniques. The steps shown can be implementedin software that is stored on a storage medium such as a disk.

Beginning in step 901, a stylus “down” event is detected. As notedpreviously, any of various input devices such as a mouse with key clicksor others can be used. In step 902, a test is performed to determinewhether the annotation mode has been enabled. (See FIG. 4). If theannotation mode is not presently active, then in step 903 processingreturns to the browser (i.e., the stylus movement command is passedthrough to document browser 801).

In step 904, after it has been determined that the annotation mode isactive, the page identifier for the currently displayed page isretrieved. It is contemplated but not necessary that each document pagehave a unique identifier (e.g., a unique URL). In step 905, a test isperformed to determine whether the currently displayed page has apreviously existing “ink” or “annotation” file associated therewith. Ifsuch an ink file exists, it is retrieved from storage area 805 (see FIG.8). If no such file exists, a new ink file is created in step 906,preferably using a name that readily corresponds to the displayeddocument page.

After an ink file has been retrieved or newly created, a test isperformed in step 907 to determine whether the annotation mode is “ink”mode. If the current annotation mode is “ink” mode, then in step 911opaque pixels are written into the ink file at the current stylusposition. The number of pixels written can be varied depending on thewidth or “swath” to be used for the annotation. For a wide swath (e.g.,a magic marker type of annotation), a plurality of pixels can be writtensurrounding the current stylus position. For a narrower swath (e.g., apinpoint type of annotation), a smaller number of pixels (e.g., onepixel wide) can be written to the annotation file at the current stylusposition. It is within the scope of the invention to permit the user toselect or change the width of the annotation marks.

In step 914, a pixel blending operation is performed, such that thepixels in the ink file are blended with pixels from the document, whichcauses the document to be displayed with annotations. (As describedabove, opaque pixels may entirely replace those in the viewed document).In step 915, a test is performed to determine whether the stylus orother input device has been lifted or disengaged. If so, then in step916 the ink layer is stored, and processing returns to the browser instep 917. Otherwise, annotations continue at step 902, and can be storedas part of the same stroke. If the user again presses the stylus orinput device against the document, then annotations resume in step 901.

Returning to step 907, if the present mode is not “ink” mode, then atest is made in step 908 to determine whether highlight mode wasselected. If highlight mode is active, then in step 912 translucentpixels are written at the current stylus position. For example, yellow,pink, or other translucent colors can be stored at the current stylusposition. As before, the pixels are blended in step 914, changing theresulting pixels on output but nevertheless permitting the user to seethe original document pixels in a modified form. Processing continues asdescribed previously.

In step 908, if highlight mode is not currently active, then in step 909a test is performed to determine whether erase mode is active. If so,then in step 913 the pixels at the current stylus position are clearedor zeroed out. As with highlight mode, the width of the erasure can bepreset to a swath wider than one pixel, and the width can be differentthan the highlight or annotation pixel width. As before, the remainingnon-erased pixels are blended with the original document image in step914 and processing continues until the ink layer is stored.

FIG. 9B shows a flowchart indicating how previously created annotationscan be superimposed over a document page. In step 918, a title changeevent is detected in document browser 801, and is sent to annotationeditor 803. In various embodiments, a title change event occurs wheneverthe presently viewed document page changes. This may occur when the userjumps to a new document page, or when the user moves forward or backwardamong a sequence of related document pages, such as might occur in abook or a set of related hyperlinks. Other types of events, such as a“status change” event, for example, can be used instead of a titlechange event.

In step 919, a test is performed to determine whether an ink layeralready exists for the new document page. If no ink layer exists for thepage, processing returns to the document browser and the page isdisplayed normally. If an ink layer exists for the page, then in step920 the ink layer is retrieved. In step 921, the pixels from theretrieved ink layer are blended with the displayed page and theresulting image appears on the computer display. Thereafter, processingreturns to the browser. A separate ink layer file can be created foreach document page, or one ink file can be created for an entiredocument and indexed according to pages on which the annotations appear.Other approaches are of course possible.

Thus has been described a system, method, and apparatus for annotatingelectronic document pages using an annotation editor that storesannotations independently of the content of the underlying document. Itwill be appreciated that many modifications and variations of theinvention are possible, and the scope of the invention is not limited bythe specific examples and descriptions herein.

We claim:
 1. A computer-implemented method of annotating pages of anelectronic document independently of the contents of the electronicdocument, the computer-implemented method comprising the steps of: (a)displaying a page of the electronic document on a computer displaydevice using a document browser that permits a user to move forward andbackward among a plurality of document pages; (b) detecting a selectionof an annotation mode that permits the user to annotate the currentlydisplayed document page; (c) receiving annotation stroke input from auser input device indicating movement associated with the user inputdevice on the currently displayed document page, wherein the user inputdevice comprises a stylus comprising a first end portion and a secondend portion; (d) storing annotation stroke data based on the receivedannotation stroke input, said annotation stroke data comprising datacorresponding to the stroke location and the movement associated withthe user input device, wherein the annotation stroke data is stored inan annotation file associated with the user, the annotation file storedseparate from the electronic document; (e) detecting whether the firstend portion of the stylus or the second end portion of the stylus isbeing moved across the computer display device; (f) if the first endportion of the stylus is being moved across the computer display device,then selecting an ink annotation mode; and (g) if the second end portionof the stylus is being moved across the computer display device, thenselecting an eraser annotation mode.
 2. The computer-implemented methodof claim 1, further comprising the step of blending pixels in theannotation file with pixels in the electronic document to cause thecomputer display device to display the electronic document withannotations.
 3. The computer-implemented method of claim 2, whereinblending pixels comprises execution of an alpha blending function.
 4. Acomputer-readable storage medium storing computer-executableinstructions that, when executed by a computer, cause the computer to:display a page of an electronic document on a display device using adocument browser that permits a user to move forward and backward amonga plurality of document pages; detect a selection of an annotation modethat permits the user to annotate a currently displayed document page;receive annotation stroke input from a user input device, wherein theuser input device is a stylus comprising a first end portion and asecond end portion, the annotation stroke input indicating movementassociated with the user input device on the currently displayeddocument page; and store annotation stroke data based on the receivedannotation stroke input, said annotation stroke data comprising datacorresponding to the stroke location and the movement associated withthe user input device, wherein the annotation stroke data is stored inan annotation file associated with the user, the annotation file storedseparately from the electronic document, wherein the computer-readablestorage medium is not a signal; detect whether the first end portion ofthe stylus or the second end portion of the stylus is being moved acrossthe display device; if the first end portion of the stylus is beingmoved across the display device, then select an ink annotation mode; andif the second end portion of the stylus is being moved across thedisplay device, then select an eraser annotation mode.
 5. Thecomputer-readable storage medium of claim 4, storing furthercomputer-executable instructions that, when executed by the computer,cause the computer to blend pixels in the annotation file with pixels inthe electronic document to cause the display device to display theelectronic document with annotations.
 6. The computer-readable storagemedium of claim 5, wherein blending pixels comprises execution of analpha blending function.
 7. A computer system for annotating pages of anelectronic document independently of the contents of the electronicdocument, the computer system comprising: a display device; a user inputdevice, comprising a stylus, wherein the stylus comprises a first endportion and a second end portion; and a computing device incommunication with the display device and the user input device, thecomputing device comprising a processor and a memory storingprocessor-executable instructions that, when executed by the processor,cause the processor to: display a page of the electronic document on thedisplay device using a document browser that permits a user to moveforward and backward among a plurality of document pages; detect aselection of an annotation mode that permits the user to annotate acurrently displayed document page; receive annotation stroke input fromthe user input device, the annotation stroke input indicating movementassociated with the user input device on the currently displayeddocument page; store annotation stroke data based on the receivedannotation stroke input, said annotation stroke data comprising datacorresponding to the stroke location and the movement associated withthe user input device, wherein the annotation stroke data is stored inan annotation file associated with the user, the annotation file storedseparately from the electronic document; detect whether the first endportion of the stylus or the second end portion of the stylus is beingmoved across the display device; if the first end portion of the stylusis being moved across the display device, then select an ink annotationmode; and if the second end portion of the stylus is being moved acrossthe display device, then select an eraser annotation mode.
 8. Thecomputer system of claim 7, wherein the memory stores furtherprocessor-executable instructions that, when executed by the processor,cause the processor to blend pixels in the annotation file with pixelsin the electronic document to cause the display device to display theelectronic document with annotations.
 9. The computer system of claim 8,wherein blending pixels comprises execution of an alpha blendingfunction.